Peening position control device of ultrasound inner wall peening system

ABSTRACT

A peening position control apparatus, includes: an ultrasonic wave generation unit generating ultrasonic waves; an ultrasonic wave radiation unit disposed to contact the ultrasonic wave generation unit, the ultrasonic wave radiation unit receiving an ultrasonic medium transmitting the ultrasonic waves therethrough; and an insert member configured to be inserted into a treatment object disposed inside the ultrasonic wave radiation unit.

TECHNICAL FIELD

The present invention relates to an ultrasonic peening system and, more particularly, to a technique of controlling peening points on an inner wall of a treatment object.

BACKGROUND ART

With reduction in size or weight of metal parts, various methods have been employed to improve fatigue strength of mechanical parts. Particularly, peening is a mechanical surface treatment process in which a surface of a metal part is blasted with a means capable of applying pressure to the surface to improve the strength of the surface. Representative examples of peening include shot peening and laser peening.

Shot peening is a process in which a surface of a treatment object is bombarded with metal particles called shot balls at high velocities to induce compressive residual stress on the surface. Here, compressive residual stress refers to stress that is present in a plastically deformed material even after all external loading forces are removed. Compressive residual stress induced on the surface of the treatment object through peening can increase fatigue life of the treatment object. Shot peening is particularly effective in increasing service life of metal machine parts subjected to bending, warping or cyclic loading. However, since shot peening cannot provide sufficient strength and fine treatment to the surface of a metal material, applicability of shot peening to precision parts is limited.

Laser peening is a process in which a coating layer is formed on a surface of a treatment object, followed by irradiation with laser beams to induce plasma, such that shock waves generated due to the pressure of the plasma can induce compressive residual stress at the surface of the treatment object. Laser peening can produce compressive residual stress to a depth of up to 10 times the depth to which compressive residual stress is produced through shot peening. However, laser peening has been limitedly applied to aircraft components due to high equipment/process costs.

In addition, since it is difficult for shot balls to reach an inner wall of a treatment object, such as an inner wall of a pipe (e.g., borehole) or sides of teeth of a gear, the angle of incidence of the shot balls is set narrowly. Further, when a treatment object having a blind hole is subjected to peening, shot balls are loaded inside the blind hole, causing insufficient peening.

DISCLOSURE Technical Problem

Embodiments of the present invention have been conceived to solve such a problem in the art and it is an aspect of the invention to provide a peening position control technique which can supply ultrasonic waves in the form of standing waves to peen an inner wall of a treatment object while controlling peening points on the inner wall of the treatment object, thereby allowing the treatment object to be uniformly peened in a selective manner.

Technical Solution

In accordance with one aspect of the present invention, a peening position control apparatus includes: an ultrasonic wave generation unit generating ultrasonic waves; an ultrasonic wave radiation unit disposed to contact the ultrasonic wave generation unit, the ultrasonic wave radiation unit receiving an ultrasonic medium transmitting the ultrasonic waves therethrough; and an insert member configured to be inserted into a treatment object disposed inside the ultrasonic wave radiation unit, wherein the insert member is inserted into the treatment object from one side of the treatment object; the ultrasonic waves generated by the ultrasonic wave generation unit are transmitted through the ultrasonic medium from the other side of the treatment object; the ultrasonic waves transmitted through the ultrasonic medium are reflected on a surface of the insert member located inside the treatment object to be converted into a standing wave inside the ultrasonic medium such that an inner wall of the treatment object is peened by the standing wave; and peening points on the inner wall of the treatment object are adjusted according to a degree of insertion of the insert member.

The peening points may correspond to pressure antinodes of the standing wave.

The inner wall of the treatment object may be peened by cavitation at points corresponding to the pressure antinodes.

The surface of the insert member located inside the treatment object may have a reflective facet formed thereon to reflect the ultrasonic waves generated by the ultrasonic wave generation unit.

The reflective facet may include a rigid body.

The treatment object may include an inner wall of a nozzle.

The insert member may include a rod.

The reflective facet may have different acoustic impedance than the ultrasonic medium such that the ultrasonic waves are reflected by the reflective facet to be amplified into a standing wave inside the ultrasonic medium.

The ultrasonic wave generation unit may be at least partially inserted into the treatment object from the other side of the treatment object.

Advantageous Effects

Embodiments of the present invention provide a peening position control apparatus which supplies ultrasonic waves in the form of a standing wave to peen an inner wall of a treatment object, wherein peening points on the inner wall of the treatment object can be controlled, thereby allowing the treatment object to be uniformly peened in a selective manner.

DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a peening position control apparatus for ultrasonic peening systems according to an embodiment of the present invention.

FIG. 2 is a plan view of a treatment object 10 and an insert member 20 shown in FIG. 1.

FIG. 3 and FIG. 4 are sectional views illustrating one exemplary operation procedure of the peening position control apparatus according to the embodiment of the present invention.

FIG. 5 and FIG. 6 are sectional views illustrating another exemplary operation procedure of the peening position control apparatus according to the embodiment of the present invention.

FIG. 7 is a sectional view of the peening position control apparatus according to the embodiment of the present invention, wherein a portion of the ultrasonic wave generation unit is inserted into the treatment object.

BEST MODE

The above and other aspects, features, and advantages of the present invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings. It should be understood that the present invention is not limited to the following embodiments and may be embodied in different ways, and that the embodiments are provided for complete disclosure and a thorough understanding of the present invention by those skilled in the art. The scope of the present invention is defined only by the claims. Like components will be denoted by like reference numerals throughout the specification.

Description of known functions and constructions which may unnecessarily obscure the subject matter of the present invention will be omitted. Further, terms to be described later are terms defined in consideration of functions of the present invention, and these may vary with the intention or practice of a user or an operator. Therefore, such terms should be defined based on the entire content disclosed herein.

Embodiments of the present invention provide an ultrasonic peening position control apparatus which can effectively peen an inner wall of a treatment object. Specifically, according to the present invention, with the treatment object disposed in an ultrasonic wave radiation unit, the inner wall of the treatment object adjoining an ultrasonic medium is peened by cavitation intensively occurring in the ultrasonic medium at pressure antinodes of a standing wave created by reflection of ultrasonic waves from an ultrasonic wave reflection facet having different acoustic impedance than the ultrasonic medium, wherein the ultrasonic wave reflection facet can be moved in the treatment object to change the positions of the pressure antinodes of the standing wave, thereby controlling peening points on the inner wall.

Here, “standing wave” refers to a combined wave produced by superposition of two sine waves having the same frequency, amplitude and wavelength and traveling through the same medium in opposite directions. Such a standing wave oscillates in time and is fixed in space. A point along the standing wave at which the wave has a pressure amplitude of 0 is referred to as a pressure node and a point along the standing wave at which the wave has a maximum pressure amplitude is referred to as a pressure antinode.

In addition, “cavitation”, as used herein, refers to formation of cavities in a medium due to generation of bubbles caused by propagation of a standing wave. The cavities formed in the medium by the standing wave generate a pressure of several hundred atmospheres or higher and high heat in a moment (in tens of milliseconds) when contacting a side of the treatment object and thus can induce compressive residual stress at the side of the treatment object, thereby peening the treatment object. More specifically, at a negative (−) pressure, the cavities grow to maximum sizes over time, and, at a positive (+) pressure, the cavities are compressed and collapse.

According to the present invention, ultrasonic waves generated by an ultrasonic wave generation unit are converted into a standing wave such that the treatment object can be peened by cavitation at points corresponding to pressure antinodes of the standing wave, and the position of the reflection facet reflecting the ultrasonic waves can be changed, thereby changing the positions of peening points corresponding to the pressure antinodes.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view of a peening position control apparatus for ultrasonic peening systems according to an embodiment of the present invention.

Referring to FIG. 1, the peening position control apparatus includes an ultrasonic wave generation unit 100 and an ultrasonic wave radiation unit 200 contacting the ultrasonic wave generation unit. The position of the ultrasonic wave generation unit 100 can be easily changed according to position of a treatment object 10, that is, a peening target. The ultrasonic wave radiation unit 200 may contact a surface of the ultrasonic wave generation unit 100 through which ultrasonic waves generated from the ultrasonic wave generation unit 100 can be easily transmitted to the ultrasonic wave radiation unit 200.

Specifically, the ultrasonic wave generation unit 100 may include a piezoelectric layer and a piezoelectric element (not shown) composed of a pair of electrodes disposed on respective opposite sides of the piezoelectric layer. The piezoelectric element is an ultrasonic transducer that resonates to generate ultrasonic waves upon receiving electric power from a power supply (not shown). More specifically, the piezoelectric element is based on the reverse piezoelectric effect in which, upon application of alternating current across the piezoelectric element, a piezoelectric material deforms such that a piezoelectric crystal repeatedly expands and contracts to create mechanical oscillation, thereby generating ultrasonic waves. The ultrasonic wave generation unit 100 may generate ultrasonic waves with an output frequency of 20 kHz to 40 kHz.

The piezoelectric layer of the piezoelectric element may be formed of, for example, at least one selected from among lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), lead zinc niobate-lead titanate (PZN-PT), lead indium niobate-lead titanate (PIN-PT), lead ytterbium niobate-lead titanate (PYN-PT), BaNiTiO₃ (BNT), barium zirconate titanate-barium calcium titanate (BZT-BCT), ceramics, and polymer composites, without being limited thereto. In addition, the pair of electrodes may be formed of any typical electrode material known in the art, for example, aluminum (Al) or silver (Ag).

The ultrasonic wave radiation unit 200 may include an ultrasonic medium 210 through which ultrasonic waves generated by the ultrasonic wave generation unit 100 are transmitted to the treatment object 10 disposed in the ultrasonic wave radiation unit 200. The ultrasonic medium 210 serves to transmit ultrasonic waves generated by the ultrasonic wave generation unit 100 to the treatment object 10 and may include, for example, water, gels, and a variety of oils. The ultrasonic wave radiation unit 200 may be completely or partially filled with the ultrasonic medium 210. Since the intensity of the cavitation described above can be reduced due to a dissolved gas in a solution constituting the ultrasonic medium 210, the ultrasonic medium 210 may be subjected to a degassing process, through which the dissolved gas in the solution is completely removed. An outer frame constituting the ultrasonic wave radiation unit 200 may be formed of any typical material known in the art, so long as the material does not affect physical properties of the ultrasonic medium 210.

The treatment object 10 may be disposed in the ultrasonic wave radiation unit 200 such that ultrasonic waves generated by the ultrasonic wave generation unit 100 are transmitted through the ultrasonic medium 210 from one side of the treatment object. The treatment object may be open at the other side thereof. For example, the treatment object may include a nozzle.

An insert member 20 may be inserted into the treatment object 10 from the other side of the treatment object 10. Ultrasonic waves transmitted through the ultrasonic medium 210 are reflected by one surface of the insert member 20, for example, a surface of the insert member 20 located inside the treatment object 10, to be converted into a standing wave in the ultrasonic medium 210, such that the inner wall of the treatment object 10 can be intensively peened at pressure antinodes of the standing wave. Here, peening points on the treatment object may correspond to the pressure antinodes of the standing wave. Thus, the inner wall of the treatment object 10 can be peened by cavitation at points corresponding to the pressure antinodes. The insert member 20 configured to be inserted into the treatment object 10 may include, for example, a rod.

An ultrasonic wave reflection facet 22 may be formed on the surface of the insert member 20 located inside the treatment object 10. The ultrasonic wave reflection facet reflects ultrasonic waves generated by the ultrasonic wave generation unit 100 to transmit the ultrasonic waves in the form of a standing wave to the treatment object 10. That is, the peening position control apparatus according to the present invention may be configured such that the ultrasonic waves are reflected by one surface of the insert member 20 (a surface of the insert member 20 located inside the treatment object 10) or may be configured such that the ultrasonic waves are reflected by the ultrasonic wave reflection facet 22 formed on the one surface of the insert member 20 to improve ultrasonic wave reflection efficiency. The ultrasonic wave reflection facet 22 may include a material having different acoustic impedance than the ultrasonic medium 210, for example, a rigid body which is not changed in shape or size even when external force is applied thereto.

FIG. 2 is a plan view of the treatment object 10 and the insert member 20 shown in FIG. 1.

Referring to FIG. 2, the treatment object 10 may be a cylindrical nozzle and the insert member 20 may be a rod that is inserted into the treatment object 10.

FIG. 3 and FIG. 4 are sectional views illustrating one exemplary operation procedure of the peening position control apparatus according to the present invention. In FIG. 3 and FIG. 4, the insert member 20 is shown as inserted into the treatment object 10 from the top of the treatment object 10.

Referring to FIG. 3, ultrasonic waves generated by the ultrasonic wave generation unit 100 are reflected by the ultrasonic wave reflection facet 22 formed on the surface of the insert member 20 located inside the treatment object 10 to be converted into a standing wave such that the inner wall of the treatment object 10 is peened by the standing wave. Points on the inner wall of the treatment object 10 which are peened in a concentrated manner may correspond to pressure antinodes of the standing wave as indicated by A of FIG. 3.

Referring to FIG. 4, the insert member 20 inserted into the treatment object 10 may be moved a predetermined distance from an initial position shown in FIG. 3.

When the insert member 20 is moved a predetermined distance in the treatment object 10, positions of pressure nodes of the standing wave with respect to a pressure node on the reflection facet 22 of the insert member 20 are all changed, such that positions of pressure antinodes of the standing wave are also changed. In FIG. 4, A′ denotes the changed positions of the pressure antinodes.

That is, movement of the insert member 20 causes change in position of the pressure node of the standing wave on the reflection facet 22 of the insert member 20 and change in position of the pressure antinodes of the standing wave, such that the treatment object can be peened at points corresponding to the pressure antinodes changed in position.

FIG. 5 and FIG. 6 are sectional views illustrating another exemplary operation procedure of the peening position control apparatus according to the present invention. Unlike in FIG. 3 and FIG. 4, in FIG. 5 and FIG. 6, the insert member 20 is shown as inserted into the treatment object 10 in the opposite direction, that is, from the bottom of the treatment object 10.

Since the operation procedure shown in FIG. 5 and FIG. 6 is substantially the same as the operation procedure shown in FIG. 3 and FIG. 4, in which the inner wall of the treatment object 10 is peened by the standing wave created by reflection of ultrasonic waves from the ultrasonic wave reflection facet 22, except that the insert member 20 is inserted into the treatment object 10 in the opposite direction, detailed description thereof will be omitted.

The insertion direction of the insert member 20 into the treatment object 10 may vary depending on the peening environment (for example, the environment under which an inner wall of a nozzle of a nuclear reactor is peened). This technical idea of the present invention will become apparent from the appended claims.

FIG. 7 is a sectional view of the peening position control apparatus according to the embodiment of the present invention, wherein a portion of the ultrasonic wave generation unit 100 is inserted into the treatment object 10.

Referring to FIG. 7, the ultrasonic wave generation unit 100 may be at least partially inserted into the treatment object 10 from a side of the treatment object 10 opposite a side of the treatment object 10 from which the insert member 20 is inserted into the treatment object 10.

When the ultrasonic wave generation unit 100 is at least partially inserted into the treatment object 10, as shown in FIG. 7, ultrasonic energy generated by the ultrasonic wave generation unit 100 can be concentrated in the interior of the treatment object 10, thereby improving peening efficiency.

Although it has been described that at least a portion of the ultrasonic wave generation unit 100 is inserted from the top of the treatment object 10 and the insert member 20 is inserted from the bottom of the treatment object 10 in FIG. 7, the opposite may be the case. That is, even when the peening position control apparatus is configured such that at least a portion of the ultrasonic wave generation unit 100 is inserted into the treatment object 10, the insertion direction of the insert member 20 into the treatment object 10 may be varied, as needed.

The embodiments of the present invention provide a peening position control apparatus which supplies ultrasonic waves in the form of a standing wave to peen an inner wall of a treatment object, wherein peening points on the inner wall of the treatment object can be controlled by changing a ultrasonic wave reflection point to change positions of pressure antinodes of the standing wave, thereby allowing the treatment object to be uniformly peened in a selective manner. 

1. A peening position control apparatus, comprising: an ultrasonic wave generation unit generating ultrasonic waves; an ultrasonic wave radiation unit disposed to contact the ultrasonic wave generation unit, the ultrasonic wave radiation unit receiving an ultrasonic medium transmitting the ultrasonic waves therethrough; and an insert member configured to be inserted into a treatment object disposed inside the ultrasonic wave radiation unit, wherein the insert member is inserted into the treatment object from one side of the treatment object; the ultrasonic waves generated by the ultrasonic wave generation unit are transmitted through the ultrasonic medium from the other side of the treatment object; the ultrasonic waves transmitted through the ultrasonic medium are reflected from a surface of the insert member located inside the treatment object to be converted into a standing wave inside the ultrasonic medium such that an inner wall of the treatment object is peened by the standing wave; and peening points on the inner wall of the treatment object are adjusted according to a degree of insertion of the insert member.
 2. The peening position control apparatus according to claim 1, wherein the peening points correspond to pressure antinodes of the standing wave.
 3. The peening position control apparatus according to claim 2, wherein the inner wall of the treatment object is peened by cavitation at points corresponding to the pressure antinodes.
 4. The peening position control apparatus according to claim 1, wherein the surface of the insert member located inside the treatment object has a reflective facet formed thereon to reflect the ultrasonic waves generated by the ultrasonic wave generation unit.
 5. The peening position control apparatus according to claim 4, wherein the reflective facet comprises a rigid body.
 6. The peening position control apparatus according to claim 1, wherein the treatment object comprises an inner wall of a nozzle.
 7. The peening position control apparatus according to claim 1, wherein the insert member comprises a rod.
 8. The peening position control apparatus according to claim 4, wherein the reflective facet has different acoustic impedance than the ultrasonic medium such that the ultrasonic waves are reflected by the reflective facet to be amplified into the standing wave inside the ultrasonic medium.
 9. The peening position control apparatus according to claim 1, wherein the ultrasonic wave generation unit is at least partially inserted into the treatment object from the other side of the treatment object. 